Device for improving the alignment accuracy of sheet-like material

ABSTRACT

The invention concerns an aligning unit ( 8 ) for sheet-like material ( 1 ), which is aligned with rotation elements ( 25 ), ( 34 ) before the passage of a conveying plane ( 9 ) with respect to the conveying direction ( 22 ) through a machine processing sheet-like material ( 1 ). The sheet-like material ( 1 ) is gripped on at least one side by the rotation elements ( 25 ), ( 34 ). The area of contact ( 36 ), ( 44 ) between the sheet-like material ( 1 ) and segmented rollers ( 25 ) aligning the latter is minimized.

[0001] The invention concerns a device for improving the alignment accuracy in the case of a sheet-like material which is aligned before further processing in a conveying plane positionally precisely with respect to its twisted position and its oblique position with respect to the machine direction.

[0002] DE 44 16 564 A1 refers to a sheet aligning device. This device for aligning a sheet moving along an essentially plane conveying path makes possible the alignment of a moving sheet in a number of orthogonal directions, for example transverse to the conveying path and in the direction of the conveying path, and for eliminating inclined positions. The device has a first roller arrangement with a first backup roller, which is mounted so that it can turn around an axis, which lies in a plane extending parallel to the plane of the conveying path, and passes essentially at a right angle to the direction of sheet transport along the conveying path. A second roller arrangement has a second backup roller, which is mounted so that it can turn around an axis which lies in a plane extending parallel to the plane of the conveying path and passes essentially at a right angle to the direction of the sheet transport along the transport path. A third roller arrangement is provided which has a third backup roller, which is mounted so that it can turn around an axis, which lies in a plane extending parallel to the plane of the conveying path, and essentially at a right angle to the direction of the sheet transport along the conveying path. A third roller arrangement, which is capable of turning around an axis which lies in a plane extending parallel to the direction of sheet transport, is movable along its rotational axis in a direction passing transverse to the conveying path. Finally, a control device is provided which is in an operating connection with the first, respectively second, respectively third roller arrangement, and optionally controls the rotation of the first and second roller arrangement, in order to align the leading edge of a sheet moving in a position located at a right angle to the direction of sheet transport along the conveying path. Further, the control direction controls the rotation and transverse motion of the third roller arrangement, in order to align the sheet moving in the direction passing transverse to the direction of the sheet transport as well as the direction in which the sheet moves along the conveying path.

[0003] The sheet alignment device known from DE 44 16 564 A1 made it possible to satisfy the required alignment accuracy only to a limited degree. In order to achieve the required alignment accuracy, a comprehensive modification of the currently known sheet alignment device is necessary, which does not appear to be economical.

[0004] In the case of sheet-processing printing presses functioning according to the offset principle the sheets are conveyed to the feed table in a overlapping arrangement, before they are aligned to side and pull guides provided in the level of the feed table. After successful alignment of the sheet-like material the latter is transferred to a preliminary gripper in the aligned condition, which accelerates the sheet-like material to machine speed and transfers it to a curved cylinder placed after the preliminary gripping device. Other alignment concepts for the most part use cylindrical rollers, to the roller core of which a rubber coating is applied. If an alignment of sheet-like material during the advance thereof is made by changing the speed between a left and right roller gripping the sheet-like material with such a configuration, the sheet-like material experiences a rotation around a turning point, which is located on the stationary roller, or during the advance is located outside the roller with the lower speed or between the two rollers. The actual point of contact between the sheet-like material and the roller is not defined; it is known only that it is located within the roller width. This uncertainty has an effect on the quality of the alignment result.

[0005] The object of the invention is to considerably improve the alignment accuracy of sheet-like material during the advance thereof in the direction of sheet travel in view of the solution known from the prior art as well as the technical problem indicated.

[0006] According to the invention this object is achieved by the features of Patent claim 1.

[0007] The advantages attainable with the solution according to the invention are to be seen above all in the fact that the smallest possible contact surface is created between upper side of the sheet-like material to be aligned and the contact surface of the alignment element because of the geometrical shape of roller core surfaces, respectively elastic coatings applied thereto, such as, for example, rubber coatings. Thus the point of contact between printing material and roller is known or at least defined essentially more accurately as compared with the solutions known from the prior art, so that the quality of the alignment can be improved considerably. The contact surface can be made smaller the more dimensionally stable the elastic material used for alignment, which in each case is in contact with the surface of the sheet-like material, can be made.

[0008] In an advantageous embodiment of the concept underlying the invention the aligning elements can be made as rollers, that is, as rotation-symmetrical bodies, which include a roller core as well as a ring-shaped coating material applied thereto. Thus, for example, the roller core can be made our of an inexpensive material, compared with the ring-shaped coating material applied thereto, further in this way it is possible to make the roller core more easily and the to shape the ring-shaped coating specifically.

[0009] In one embodiment version the ring-shaped coating on the peripheral surface of the roller core can be applied as a liquid under pressure. In this embodiment the ring surface can be made, for example as an endless ring, which can be gripped simply on the peripheral surface of the roller core. The coating also can be glued or cast onto the surface of the roller.

[0010] In a second embodiment the ring-shaped coating on the peripheral surface of the roller core can be applied positively locking. Preferably the annularly configured coating is made in one piece, so that no interruptions, but a continuous surface, can be made on the circumference of the roller core. The annular coating can be provided, for example, with a trapezoidal cross-section, which is distinguished in particular by a narrow and sharp-edged contact area between gently tapering edges for the upper side of the sheet-like material. The more point-like, respectively linear the contact point can be made, the more exactly can alignment results be achieved with the solution according to the invention.

[0011] If ring-like coatings are applied form-locking to the peripheral surfaces of the roller core, recesses for form-locking holding of these support elements can be included in the surfaces of the roller cores. The contact elements aligning the sheet-like material can be made in the surfaces of the roller cores as annular longitudinal grooves, thus ensuring support of the support elements to be introduced into this recess on the lateral surfaces thereof.

[0012] In order to eliminate the danger of damage to the contact areas between sheet-like material and the alignment elements, the latter are configured as narrow rings or as trapezoidal surfaces, and can be made as an elastic flexible material.

[0013] In a preferred use of the solution proposed according to the invention, in order to improve the alignment accuracy the latter can be placed in an aligning unit which can be located in front of a press, for example a sheet-processing printing press. The solution according to the invention can be used in aligning units which also can be used on digitally operating rotary printing presses, since the printing material processed there, be it films, cardboard, paper, or the like, also needs alignment before it is printed or, in a given case, processed in a digitally operating machine.

[0014] The invention is explained in greater detail below by means of a drawing.

[0015] Here:

[0016]FIG. 1 shows a position deviation of a printed image which occurs relative to the printing material surface receiving the image,

[0017]FIG. 2 shows an offset of the printing image on the sheet-like material, characterized by a rotational offset,

[0018]FIG. 3 shows an offset of the printing image printed on the underside of a sheet-like material in first and perfecting form,

[0019]FIG. 4 shows the side view of a sheet intake area of a sheet-processing machine in a schematic representation,

[0020]FIG. 5 shows the top view of the alignment components, the sensors, as well as the drive for the sheet-like material relative to the sheet direction of aligning rotation elements,

[0021]FIG. 6 shows the rotation elements made over the conveying plane of the sheet-like material as segmented rollers,

[0022]FIG. 7 shows the alignment of a sheet-like material with the drives of the segmented rollers performing the alignment, and

[0023]FIG. 8 shows the configuration of the segmented rollers aligning the sheet-like material proposed according to the invention.

[0024] A rectangular oriented sheet-like material, for example a printing sheet 1, follows from the representation given in FIG. 1. The printing sheet 1 contains on its surface a printed image 2, which is surrounded by a frame-like edge 3. The deviations of ?x, respectively ?y, marked within the printing surface 2 and the frame 3, designating the position errors in the x and y directions 4, respectively 5, can appear at the time of printing the image 2 onto the surface of the sheet 1. The deviations designates with reference numbers 4, respectively 5, are position deviations, whereas in the representation shown in FIG. 2, angular deviations of the printed image 2 are shown with respect to their position on the printing sheet 1.

[0025] The angular errors ?Ø which occur are designated with reference numbers 6 in the representation shown in FIG. 2. The printing image 2 can be printed in the indicated position onto the surface of the printing material, the latter being conveyed in the direction of feed 22 with its leading edge 23.

[0026] The representation given in FIG. 3 in a schematic view shows the turning register, the offsets which occur in each case between the printed images 2 on the front and back side of the sheet-like material 1, being indicated with reference numbers 7. These are designated in the representation shown in FIG. 3 with reference numbers 7, respectively with ?x and ?y. The turning register plays a role, in particular in the case of transparent types of paper as well as in brochure printing.

[0027] The interface of sheet alignment and feeding onto a conveyor belt in a schematically presented side view follow from FIG. 4.

[0028] An aligning unit 8 is connected in front of a conveyor belt 10, onto the surface of which the sheet-like material 1 is applied in the conveying plane 9, revolving around a take-up roller 11, respectively a control roller 12. After passing through the aligning unit 8, which is described in greater detail below, the aligned sheet-like material 1 reaches the surface of the conveyor belt 10 in the conveying plane 9. After passing the take-up roller 11 the sheet-like material 1 is acted upon by means of an adjusting flap 13 or adjusting lip, which is movable in the adjusting direction 13. The adjusting lip or adjusting flap 13 can be a plastic component, which can be brought from one adjusted position 13.1 into an adjusted position 13.2, which is shown here only schematically in solid or dashed lines. By means of the adjusting flap or adjusting lip 13 the sheet-like material 1 is pressed onto the surface of the conveyor belt 10 in the aligned condition of the sheet-like material 1. After passage of the pressing element, the sheet held on the surface of the conveyor belt 10 passes a charging unit 14. An electrode 15, which gives the sheet-like material 1 a static charge and thus provides for its adhesion to the surface of the conveyor belt, is held in this charging unit 14 within a hood-like cover.

[0029] A leading edge sensor 17 is located after the charging unit 14, which is shown only schematically in FIG. 4. This sensor consists of a radiation source 18, in front of which there is a lens arrangement, located under the conveying plane 9. The radiation field 20 issuing from the lens arrangement 19 penetrates the conveying plane 9 and strikes a diaphragm arrangement, which is provided above the conveying plane 9 of the sheet-like material 1. A receiver 21, which senses the presence of the leading edge 23 of the sheet-like material 1, is located behind the diaphragm arrangement.

[0030] The aligning unit 8, the components of which are shown here is a schematic representation, follows from the top view of FIG. 4. The aligning unit 8 is reached by the sheet-like material 1, which is conveyed in the conveying direction 22. The leading edge 23 of the sheet-like material I is offset in relation to the conveying direction 22 of the sheet-like material 1, which results in an oblique course of the side edges 24 of the sheet-like material 1. As soon as the leading edge 23 of the sheet lying in oblique position with respect to the conveying direction 22 passes over a first light barrier 26, the drives 27, designated as M1, respectively M2, which drive rotation elements 25 over individual axes 32, are accelerated to advance speed. By means of the control of the drives 27, M1, or M2, released via the light barrier 26 it is assured that each copy of the sheet-like material 1 comes into contact with identical circumferential steps of the rotation elements 25, which can be made, for example, as segmented rollers. Any differences occurring in the advance motion, which could be attributed to dimension and shape tolerances of the two rotation elements 25, in this way appear in the case of each copy of the sheet-like material 1 and can be easily calibrated.

[0031] After the two rotation elements 25 are set into rotation by passing the first light barrier 26, the sheet-like material 1 is transported over a further sensor unit 30.1 located after the first light barrier 26. As soon as the first of the two sensors of the sensor pair 30.1 has detected the leading edge 23 of the sheet-like material 1, a counting unit begins to count the motor steps. The counting process ends, and the difference is determined, when the second sensor of the sensor pair 30.1 switches on.

[0032] From the counter state determined in this way a contact value is determined which is given as an additional advance to the last started segmented roller drive, that is, either the drive 27, which is designated as M1, or the drive 27, which is designated as M2. In this way the rotation body 25, made correspondingly as a segmented roller, is moved with increased advance speed, until the predetermined path difference is completely compensated. At the end of this correction process the leading edge 23 of the sheet is oriented exactly perpendicular to the conveying direction 22.

[0033] After successful correction the sheet-like material 1 is transferred in the conveying direction 22 passing from the first pair of segmented rollers 25 to the following pair of bodies of rotation 25, which can be held on a common axis 31. Now the segmented roller pair 25 driven via drive 27, respectively M1 and M2, can be disengaged and a resting position is achieved.

[0034] The sheet-like material 1 now correctly aligned with respect to its angular position now passes onto a sensor field 30, in which the position of the side edges 24 of the sheet-like material 1 is measured. From the measured value determined a position change for the drive 27 is determined, which is designated as M4, the drive shaft of which extends parallel to the sheet travel direction 22. A correction of the position of the sheet-like material 1 parallel to is conveying direction 22 (see FIG. 7) by means of this drive 27 held in a second orientation 29.

[0035] Then the sheet-like material 1 oriented in is angular position and its lateral position passes under an adjusting flap or adjusting lip element 13 set in a position 13.1 or 13.2 on the conveyor belt 10, in order to pass into the next printing unit in correctly oriented position. An embodiment of rotation element 25 located above the conveying plane 9, held in the aligning unit 8, follows from the representation according to FIG. 6. The rotation elements 25 can be made in preferred embodiment as segmented rollers, which have a peripheral surface 33 characterized by an interruption. The segmented rollers 25 rotate in the direction 34, characterized by the arrow shown and describe approximately a ¾ circle with respect to its rotation axis. A roller supporting the sheet-like material 1 is shown under the respective segmented roller 25. This can be in one part or also consist of a roller core 38, or a coating 35, 37, see FIG. 8.

[0036] The bodies of rotation serving as segmented rollers 25 are show in a resting position in the left-hand part of FIG. 6, while in the right-hand part of FIG. 6 they grip a copy of the sheet-like material 1 conveyed in the conveying direction 22 with its peripheral surface 33 and transport it corresponding to the direction of rotation 34 in the sheet travel direction 22. FIG. 5 shows the correction of the angular position of the sheet-like material 1 during the passage of the aligning unit 8. In the position of the sheet-like material 1 shown in FIG. 7, the leading edge thereof 23 just reaches the last sensor of the sensor pair 30.1, so that now the drive 27 of the segmented roller 25 designated as M1 can be accelerated, in order to compensate the angular position of the sheet-like material 1 with respect to the conveying direction 22. It should be mentioned that, as opposed to the drives M3 and M4, which are connected with one another via a continuous drive shaft 31, the segmented rollers 25, which are connected with drives M1 and M2, in each case are driven via individual shafts 32. After correction of the angular position of the sheet-like material 1 by controls of the respective drive 27 (M1 and M2) of the segmented rollers 25 with different speeds, the sheet-like material 1 experiences a correction of its lateral position. After the measurement of the position of the side edges 30 of the sheet-like material 1 by the sensors 31, the sheet-like material 1 now is oriented correctly parallel to the conveying direction 11, by moving the sheet-like material 1 into its conveying plane before reaching the adjusting element 13 and before passing onto the conveyor belt 10 via the drive M4. The advance of the sheet-like material 1 is ensured via a common shaft 31, with drive M3, oriented in the first orientation 28 with a correctly aligned leading edge 23, while the latter is oriented in its later position via the drive 27, designated as M4, held in a second orientation 29.

[0037] The configuration of the segmented rollers, which can be made in two parts according to an embodiment shown, follows from FIG. 8. The aligning elements made as segmented rollers 25 can be provided with a coating 35. A ring-like coating 35 with cylindrical contact surface 45 is shown in the left embodiment according to FIG. 8.

[0038] On the other hand, the middle embodiment has a roller core 38, onto the peripheral surface of which a trapezoidal coating 37 is mounted. The trapezoidal coating 37 can consist of rubber or of another elastic material and be applied form-locking on the surface of the roller core 38 or also be cast on the latter. It can be simply glued or shrunk as an endless ring on the circumference. In order to increase the dimensional stability, the edge angles 39 of the trapezoidal coating 37 are made as attachments 39 with a shallow inclination.

[0039] A bar-like contact area 36 extending in the peripheral direction of the trapezoidal coating 37 is made between the two edges 39. The point of contact between one side of the sheet-like material 1 and the contact surface 36 can be held very small and defined very exactly by means of the narrow contact area, by means of which a sheet-like material 1 in each case to be aligned by the contact areas 36, since the turning point, around which the alignment is made, now is defined.

[0040] In the case of aligning elements with smooth cylinder surfaces of 35 the actual turning point is not known, the latter is found over the width of the roller core at a point on the contact surface 45, not defined more closely. As an alternative to a coating carrier made in ring-shape, which can also be applied form-locking onto the peripheral surface of a roller core 38, a coating element also can be held interlocking on the roller core 38. According to the right-hand representation in FIG. 8 a ring-shaped recess 41 in the form of a longitudinal groove can be made on the peripheral surface of a roller core 38. The longitudinal groove is made out of a groove base 42 extending in each case in ring shape on the roller core 38 and bounded by two groove edges also extending in ring shape on the roller core 38. A rubber filling 40 or a ring-shaped, trapezoidal, rectangular, lozenge-shaped, or a cylindrically configured aligning element can be held in a recess on the circumference of the roller core 38 configured in this way. The walls 42 of the recess 41 supporting the side edges of an aligning element 40 configured in this way permit a high dimensional stability with the smallest possible width of the bearing surface 45 of the aligning element. This assures that in the case of the motions of the sheet-like material 1 and the aligning element 25 which occur, the contact surface 45in not pushed out of the recess 41 during the lateral alignment. For this it is sufficient that according to the right-hand embodiment in FIG. 8, the contact surface 45 projects by only a few tenths of a millimeter over the surface 46 of the roller core 38. By gripping the sheet-like material (1) the alignment elements 40 are slightly compressed, resulting in a smooth, continuous surface with the adjacent surface 46 of the roller core 38. The friction value with appears between the sheet-like material 1 and the surface of the aligning element 25 can be influenced by means of the choice of material for the aligning element, which is introduced into the recess 41 of the segmented roller core 38. The friction value on the underside must be less than the friction value which occurs between the upper side of the sheet-like material 1 and the peripheral surfaces 33 of the segmented rollers 25, so that an alignment relative to the counter-pressure elements supporting the sheet-like material 1 can take place by means of the segmented rollers.

[0041] Instead of an aligning element to be introduced into the surface of the roller core 38 itself also can be configured correspondingly, so that on the outermost end thereof there is a contact surface touching the upper side of the sheet-like material 1 linearly, which is causal for an exact alignment result.

REFERENCE NUMBER LIST

[0042] 1 sheet-like material

[0043] 2 printing image

[0044] 3 frame

[0045] 4 position error y-direction

[0046] 5 position error x-direction

[0047] 6 twisting error

[0048] 7 front side/rear side offset

[0049] 8 aligning unit

[0050] 9 conveying plane

[0051] 10 conveyor belt

[0052] 11 backup roller

[0053] 12 control roller

[0054] 13 adjusting element

[0055] 13.1 1^(st) position

[0056] 13.2 2_(nd) position

[0057] 14 charging unit

[0058] 15 electrode

[0059] 16 support

[0060] 17 leading edge sensor

[0061] 18 radiation source

[0062] 19 lens

[0063] 20 radiation field

[0064] 21 receiver

[0065] 22 machine direction

[0066] 23 leading edge

[0067] 24 side edge

[0068] 25 segmented roller

[0069] 26 light barrier

[0070] 27 segmented roller drive

[0071] 28.1 drive orientation

[0072] 28.2 drive orientation

[0073] 30 sensor field

[0074] 30.1 sensor pair

[0075] 31 common shaft

[0076] 32 individual shaft

[0077] 33 segmented roller circumference

[0078] 34 counter-pressure element

[0079] 35 ring-shaped coating

[0080] 36 contact area

[0081] 37 trapezoidal coating

[0082] 38 roller core

[0083] 39 sides

[0084] 40 rubber filling

[0085] 41 groove

[0086] 42 groove bottom

[0087] 43 groove edges

[0088] 44 bearing surface width

[0089] 45 surface—roller core contact surface 

1. An alignment unit for sheet-like material (1), which is aligned with rotation elements (25), (34) before passing a conveying plane (9) with respect to the conveying direction (22) through a machine processing sheet-like material (2) and is gripped on at least one side of the rotation elements (25), (34), wherein the contact area (36), (44) is minimized between segmented rollers (25) aligning the sheet-like material (1) and the sheet-like material(1).
 2. The aligning unit according to claim 1, wherein the segmented rollers (25) have a roller core (38) as well as a ring-shaped coating (35).
 3. The aligning element according to claim 2, wherein the ring-shaped coating (35) is held on the peripheral surface of the roller core (38) force locking.
 4. The aligning unit according to claim 2, wherein the ring-shaped coating (4) on the peripheral surface (46) of the roller core (38) is held form locking.
 5. The aligning unit according to claim 2, wherein the ring-shaped coating (35) is made in one piece.
 6. The aligning unit according to claim 2, wherein the ring-shaped coating (35) has a trapezoidal cross-section (37).
 7. The aligning unit according to claim 1, wherein the surface (46) or the roller core (38) is shaped as a trapezoid.
 8. The aligning unit according to claim 4, wherein the roller core (38) has a recess (41) for form-locking holding of an elastic aligning element (40).
 9. The aligning unit according to claim 8, wherein the aligning element (4) is inserted in ring-shape into the recess (41).
 10. The aligning unit according to claim 8, wherein the aligning element (40) is flanked by lateral surfaces (43) of the recess (41).
 10. Aligning unit according to claim 8, wherein the aligning element (40) is flanked by side surfaces (43) of the recess (41).
 11. A press with an aligning unit (8) for sheet-like material (1), which is aligned with rotation elements (25), (34) in front of the passage of a conveying plane (9) with respect to its conveying direction (22) through a machine processing sheet-like material (1) and at least one side is gripped by the rotation elements (25), (34), wherein the contact area (36), (44) between the segmented rollers (25) aligning the sheet-like material (1) and the sheet-like material (1).
 12. A sheet-processing machine with an aligning unit (8) for sheet-like material (1), which is aligned with rotation elements (25), (34) before the passage of a conveying plane (9) in relation to its conveying direction (22) through a machine processing sheet-like material (1) and is gripped on at least one side by the rotation elements (25), (34), wherein the contact area (36), (44) between the segmented rollers (25) aligning the sheet-like material (1) and the sheet-like material (1) is minimized.
 13. A digital printing press with an aligning unit (8) for sheet-like material (1), which is aligned with rotation elements (25), (34) before passing a conveying plane (9) with respect to its conveying direction (22) through a machine processing sheet-like material (1) and is gripped by the rotation elements (25), (34) on at least one side, wherein the contact area (36), (44) between the segmented rollers (25) aligning the sheet-like material (1) and the sheet-like material (1) is minimized. 